Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Sub-cooling or under-cooling

Normal cooling

Super-cooling

None of these

2. The boiling point of ammonia is

-77.7°C

-10.5°C

-33.3°C

-30°C

3. Most thermostatic expansion valves are set for a superheat of

5°C

15°C

10°C

20°C

4. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Dew point temperature

Relative humidity

5. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

6. The capillary tube, as an expansion device, is used in

Water coolers

All of these

Domestic refrigerators

Room air conditioners

7. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Rankine

Reversed Carnot

8. Freon group of refrigerants are

Toxic

Inflammable

Nontoxic and non-inflammable

Non-inflammable and toxic

9. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

10. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Dry saturated vapour

Superheated vapour

Wet vapour

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11. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

12. A bootstrap air cooling system has

Three heat exchangers

Four heat exchangers

Two heat exchangers

One heat exchanger

13. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.67

0.376

0.6

14. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

2 bar

15 bar

8 bar

15. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

4.33

3.33

1.33

16. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Superheat the vapour

17. The domestic refrigerator uses following type of compressor

Centrifugal

Piston type reciprocating

Miniature sealed unit

Axial

18. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

1: 3

1: 1

9: 1

19. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

20. Which of the following cycles uses air as the refrigerant?

Bell Coleman

Stirling

Ericson

Carnot

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21. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-56.6°C

-77.7°C

22. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

40 tons

5 tons

23. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

24. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

25. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

26. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

27. Highest temperature encountered in refrigeration cycle should be

Near critical temperature of refrigerant

At critical Temperature

Much below critical temperature

Above critical temperature

28. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

29. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Ammonia

Freon

Carbon dioxide

Brine

30. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

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31. For obtaining high COP, the pressure range of compressor should be

Any value

High

Low

Optimum

32. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

None of these

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

33. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

Condenser

34. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

35. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Large latent heat

High risibility with oil

Good electrical conductor

36. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

Takes place at constant temperature

37. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Always more than unity

Any one of the above

Equal to unity

38. Critical temperature is the temperature above which

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

A gas will never liquefy

39. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Positive

Zero

Negative

40. The minimum temperature to which water can be cooled in a cooling tower is

Wet bulb temperature of air

Dew point temperature of air

Ambient air temperature

Dry bulb temperature of air

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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